Saw a friends almost completed home today and his sub panel has the ground and neutural bonded. He has a main panel in basement with g/n bonded and sub panel on main floor with same. 4 wires into both. Should the neutural be isolated from the ground and why is it dangerous in this manner.Thanks
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All Sub Panels require SER cable, i.e. isolated ( insulated )neutral and ground
neutral and ground are only bonded at service equipment
"All Sub Panels require SER cable, i.e. isolated ( insulated )neutral and ground"No on several points.First it does not require SE cable of any type.There are other wiring systems, such as conduit, that can be used.And secondly SER cable is not sufficient.It has to be 3 CONDUCTOR plus ground.SE, type R just means that it is round with a separate ground conductor rather than having the ground strands wrapped around the insulated conductors.Don't know if they make any 3 conductor plus ground SE, but they do make TWO CONDUCTOR, with ground SE, type R.http://www.cable.alcan.com/NR/rdonlyres/0D7E3254-803E-4F52-912F-669A2DD4A66C/0/serw.pdf
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
re: your tagline .....yes, you are an A$$holeyou know full well that type SE cable is only availible as 2 conductor, with a bare groundan Intelligent person would grasp that the reason to use type SER, is to have the THREE INSULATED CONDUCTORS that you know full well would be required, and are not made as SEU cableand yes you may use conduit, with the appropriate INSULATED NEUTRAL, if your g ay a$$ , and checkbook can afford that method .....man, you are Soooooo f'n ...Smart .....I am ...totally impressedwhat's Your Liscense # ..??mines # 3346Edited 9/13/2007 11:18 pm ET by Clear_River_ConstructionEdited 9/13/2007 11:28 pm ET by Clear_River_Construction
Edited 9/13/2007 11:29 pm ET by Clear_River_Construction
You said:"yes you may use conduit, with the appropriate INSULATED NEUTRAL, if your g ay a$$ , and checkbook can afford that method ....."That's a little over the top comment. I have installed many sub panels in residential work with conduit and copper wire. It depends on physical layout whether SER cable will be legal. i.e. it isn't legal exposed on finished interior surfaces. Not that conduit looks great, but that is another story....Frank DuVal
How did I miss this the first time around."yes, you are an A$$hole"Thank you for the compliment."you know full well that type SE cable is only availible as 2 conductor, with a bare ground"Well me have another mind reader in the crowd. Someone that knows EXACTLY WHAT I KNOW. But can even read a simple sentence."Don't know if they make any 3 conductor plus ground SE, but they do make TWO CONDUCTOR, with ground SE, type R."So how do you know that I know something when I said that I didn't know it?"and yes you may use conduit, with the appropriate INSULATED NEUTRAL, if your g ay a$$ , and checkbook can afford that method ....."A REAL pro would looks at ALL of the conditions envolved and selects the appropriate wiring method and does not automatically select one.PS this also made me go back to your orginal message."All Sub Panels require SER cable, i.e. isolated ( insulated )neutral and groundneutral and ground are only bonded at service equipment"That is not true. ALL sub-panels don't require seperate neutralls and ground and in some cases the neutral and ground can be bonded together at the sub-panel.Maybe you will learn something if you go back to the code books and see where that applies..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Edited 9/15/2007 12:20 pm by BillHartmann
don't call an Auxiliary panel, metallically grounded to the Service Equipment, a Sub Panel...now if you ae Talkin', fed from a service, located in a remote structure, the ground can be a Rod, at that point, but Neutral and Ground still isolatedany other panel located in the same structure, must have the Neutral, and ground isolated, with an Insulated Neutral Conductor ..I asked ..what is Your Liscense number, and what City, just so we know Your qualifications on this subject
fed from a service, located in a remote structure, the ground can be a Rod, at that point, but Neutral and Ground still isolated
A free-standing separate structure? Doesn't necessarily require isolation of neutral and ground.
If there is no other metallic piping or pathway from the original building to the remote building, then it can be treated like a service entrance, i.e. 2 hot conductors and 1 grounded conductor, with local grounding (rods or Ufer or whatever) at the remote building. And neutral/ground bonding in the panel. Section 250.32 B(2) of the NEC.
If a separate grounding conductor is run from the first building, then the grounds and neutrals in the remote building must be isolated from each other. Section 250.32 B(1) of the NEC. And it also needs a grounding electrode (as you said).
Ed
Edited 9/15/2007 3:31 pm ET by edlee
Easy there fella. Bill's been a wealth of information on this board for many years. IF he made a mistake, there's no reason to get testy about it.
I'd not get too carried away with that 'separate structure' idea. Sure, it's OK, right now, as we speak ... only if there are NO other connections between the buildings. A fence anchored at each building could provide that secondary path. That's why I advise against doing things that way. The issue will soon become moot; the 2008 edition of the NEC has some changes in the wording, that make it clear that a separate building will need both a ground rod AND a ground wire back to the service. I've seen enough of Bill's posts to trust his judgment on electrical topics. Not that he and I never disagree; but out differences are more the result of our looking at things from a different perspective, than a question of competence.Reno, Nevada State 34024, City 05-00083, IAEI since 1967.
if you pick a position, you must defend itthere is waaay to much in the way of poor practice "advice" given out on the internetsome is dangerous ......Sub Panels have the potential for exactly that.....
Edited 9/15/2007 3:46 pm ET by Clear_River_Construction
I'd not get too carried away with that 'separate structure' idea.
Are you talking to me? I like the 3-wire outbuilding system. It's been good for the past 100 years and if it's being eliminated in the 2008 code, well that's disappointing.
I would prefer a ground-fault to clear right through the local panel rather than have to travel all the way back to another building.
I'll make more money though :-)
Ed
Just to be clear regardless of whether a 3 or 4 wire circuit is run to a sub-panel in an detached structure a grounding electrode system is required..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yeah, the neutral and the ground should be isolated at the panel. Generally this requires that a separate grounding buss be installed in the panel and the green screw that ties the neutral bus to the box must be removed. All neutral wires are attached to the neutral bus and all ground wires to the ground bus.
As it was explained to me by an electrical inspector, if a common buss is used for both and something happens to the cable providing power to the sub-panel and the neutral conductor becomes defective, the power will still flow with the ground line serving as the neutral connector to the main panel. The problem with this is that the ground wire is not insulated and is smaller than the neutral wire; in other words, it is not rated to carry that much amperage. It may overheat and cause a fire.
If you isolate the busses and the neutral wire becomes defective, nothing will work. With any luck, that will cause you to fix it.
George Patterson
Edited 9/12/2007 11:55 pm ET by grpphoto
If you isolate the busses and the neutral wire becomes defective, nothing will work
Wrong.
You'll get 240v across the system with no 120v return path. Strange obvious things will happen to your lights and appliances. It's referred to as "loose neutral".
Edited 9/13/2007 7:03 am ET by edlee
And if you have no 120v return path, none of your 120v outlets or lights will work.George Patterson
"And if you have no 120v return path, none of your 120v outlets or lights will work."They will work, just not properly.All it takes is loads on 2 circuits on different legs.And with a large number of things that are always drawing power, such a furance transformers, door bell transfers, charger power supplies, clocks/timers, and "always on" equipment it would be very, very rare that you would only have a device on one circuit drawing current at any one time..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
As one tenant said "when I turn on my stove, the fridge works". Except in this case it was one of the hots that was out. Like you said, just because it's not "working" doesn't mean it won't work. (Three edits and now I think I've expressed it clearly.LOL)
Edited 9/14/2007 7:41 pm ET by sisyphus
Edited 9/14/2007 8:06 pm ET by sisyphus
Edited 9/14/2007 8:26 pm ET by sisyphus
Art;
I once read that a frequently asked question at the public tours of the Grand Coulee Dam generating facility is: "What do they do with the water after they've taken all the electricity out of it?"
As I think about it, though, I don't know if I've ever heard the answer to that....please help me out here!
:-)
They have it shipped out to the ocean where it is dumped!Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
Sounds like an environmental disaster in the making -
uncontrolled dumping of ion-stripped waste dihydrogen monoxide.
Don
And if you have no 120v return path, none of your 120v outlets or lights will work.
Not true, as Mr. Hartmann points out.
The reason being, all of the 120v circuits are connected to each other via their branch circuit neutrals: they all tie in together at the same bussbar, agreed? So when you lose the center-tap neutral feed, these things are now in series across the 2 legs of the 240v with the interconnected white wires now completing the 240v circuit.
The result is a string of appliances and lights,etc. connected in combination series/parallel circuitry to 240v. This creates an unpredictable mix of voltage drops from 240v down across individual loads and can cause some real damage.
Edit to add: Slide down to about the middle of the page of this link, where they add a neutral into the 240v circuit, and you'll see how they're interconnected. The next diagram shows a transformer connection to a 120/240v setup.
http://www.allaboutcircuits.com/vol_2/chpt_10/1.html#02168.png
Ed
Edited 9/14/2007 4:26 pm ET by edlee
There's nothing quite like an empirical experiment to settle things. This morning, I went down to my shop, cut the power, and disconnected the neutral line to my subpanel. Turned the power on, and none of the 110 volt lines worked. At least, nothing worked as long as only one item was on. As soon as I turned two of them on at the same time, they worked fine.So. You guys are right (but you knew that).George Patterson
it was explained to me by an electrical inspector, if a common buss is used for both and something happens to the cable providing power to the sub-panel and the neutral conductor becomes defective, the power will still flow with the ground line serving as the neutral connector to the main panel. The problem with this is that the ground wire is not insulated and is smaller than the neutral wire; in other words, it is not rated to carry that much amperage. It may overheat and cause a fire.
That sir is the most absurd explanation for this practice that I have heard. Where did this so-called inspector get his certification.......from a box of Cracker Jacks?
It reminds me of a couple of other things that people have earnestly explained: northern lights are a result of the midnight sun reflecting off of the ice of glaciers at the North Pole; that a cordless drill can reverse direction because when you charge it with AC current, it saves the 2 halves of the wave and uses one for forward and the other for reverse,
To understand grounding and bonding I recommend you check out the classic book by Soares http://www.amazon.com/SOARES-Book-Grounding-Bonding-9th/dp/1890659363/ref=pd_bbs_sr_1/104-6689005-3407106?ie=UTF8&s=books&qid=1189682927&sr=1-1
This book is used by many people in the electrical field. It is surprisingly readable and interesting.
Respectfully submitted,
Ed
Edited 9/13/2007 7:30 am ET by edlee
a cordless drill can reverse direction because when you charge it with AC current, it saves the 2 halves of the wave and uses one for forward and the other for reverse,
PRICELESS, had never heard that before, now I understand!
Why do we keep the neutral and the ground separated? Look at it this way:
Electricity takes ALL paths. It seeks to go 'home' to it's source. As I mentioned in another thread, this source is usually the power company - and not the dirt beneath our feet.
The neutral serves to return "used" electricity to it's 'home.' That is, the neutral wire is normally carrying current. Even though your meter may show "0" volts, current is flowing. That's why you see a spark when you open the neutral connection - and the 'upstream' side becomes 'hot!'
The ground is like a drain pan, intended to catch any leakage and return it home in an efficient way. This will -we hope- cause the breaker to trip, and shut off the power. The point is, the ground does NOT normally carry current, or have electricity present on it.
If you connect the ground and neutral in more than one place, all the grounds become, in effect, another current carrying conductor. Another neutral, as it were. Open the 'real' neutral, and all the current will flow through the ground. The metal panels and machines you have bonded to the ground will become 'hot.' Breakers will NOT trip, because the current that flows will be the normal operating current that the appliance uses.
Remember: While most breakers are at least 15 amps .... it takes less than a tenth of an amp to kill.
That's why we connect the neutral and ground at only one place - and that place is as close to the service entrance as possible.
"If you connect the ground and neutral in more than one place, all the grounds become, in effect, another current carrying conductor. Another neutral, as it were. Open the 'real' neutral, and all the current will flow through the ground. The metal panels and machines you have bonded to the ground will become 'hot.' Breakers will NOT trip, because the current that flows will be the normal operating current that the appliance uses."
I always wondered about this. Nice explaination.
Mike HennessyPittsburgh, PA
Renosteinke,
Damm Dude!
That is the best written "Layman's" description I ever heard!
I know how to follow the rules, but understanding the why's and what for's is a big deal to me.
I've tortured my self reading stuff over and over trying to get my head around it.
You did it in 6 paragraphs!
This one is going in my notes!
Bill
I was gonna thank you for a clear, concise explaination but I see others already have so I won't bother. Oops, too late. I understand the principles, but your explaination brought it to life. Nice work.
I really appreciate the positive feedback. You would not believe how angry my wife gets when someone criticizes me; according to her, that's HER job. :D